You don't need cash. But again, you have to be very careful. Because if you only own TSLA, as TSLA drops, not only will your margin go down, but the margin requirement will go way up. I nearly lost everything a couple years ago in that exact scenario. I am not selling any PUTS after Dec 21 in case the SP drops hard after inclusion. If you do get a margin call, you can call the broker and buy deep in the money Puts cheaply that will expire worthless to make the margin call go away (I learned that too).Do you need to have any cash at hand at all, or it is enough to stay well within your allowed margin?